Three-dimensional loss reduction and improving efficiency and stall margin of axial flow compressors are still technical issues in designing compressor blades and vanes. Three-dimensional losses limit the pressure rise capability of the compressor. Such losses result e.g. from flow separation in suction surface, endwall corners, leakage around the tip, and secondary flow regions. Optimising efficiency and stall margin always involves a compromise since increasing efficiency usually reduces stall margins and increasing stall margins usually reduces efficiency.
There are numerous documents which describe approaches to reduce three-dimensional losses and/or to improve efficiency and stall margin.
Axial compressors with end bends have been proposed by Robinson et al., ASME 89-GT-6, D. Wisler, ASME journal of engineering for gas turbine and power, volume 107, April 1985, and R. F. Behlke, ASME 85-IGT-9 in order to improve performance of axial flow compressors. Bowed stator vanes have been proposed by H. Weingold et al., ASME 95-GT-380 for reduction of compressor stator end wall losses. S. Gallimore et al., ASME GT-2002-30328 as well as S. Gallimore et al. GT-2002-30329 have proposed to use airfoil sweep and dihedral in multistage axial flow compressors in order to address the above mentioned issues.
EP 0 441 097 B1 describes a compressor airfoil with bowed leading and trailing edges for reducing aerodynamic losses.
A compressor stator vane with a narrow section between its root and its tip is disclosed in EP 098092 A2. The vane may also be bowed at its trailing edge in cooperation with a narrow waist.
EP 0 704 602 B1 and EP 1 259 711 B1 describe airfoils having a leading edge with a sweep and a straight trailing edge.
EP 0 833 060 B1 describes a blade for an axial fluid machine in which the leading edge is bowed and scalloped and the trailing edge is bowed.
EP 1 505 302 A1 describes a compressor airfoil with at least a bowed leading edge.
U.S. Pat. No. 6,299,412 B1 describes bowed compressor airfoils.